RSS Feed

Angular Velocity

Rowden Fullen (1990’s)

Look at the skater spinning on the point of one skate. The original momentum continues to spin him, if he holds his arms outstretched, until friction gradually slows him down. However if the arms are drawn in and folded across the chest the speed of rotation (angular velocity) is markedly increased.

What concerns us here is the centre of gravity of the arm in relation to the speed of rotation. At the original angular velocity the centre of gravity of the arm will traverse a certain circular distance in a given time period. However when the arm’s centre of gravity is drawn in towards the centre of rotation, it follows a circular path of smaller radius and shorter circumference. Therefore if the body were to rotate at the same angular velocity, the distance traversed by the arm’s centre of gravity would be much smaller in the given time period — which is not possible under the law of conservation of angular momentum.

Discounting the outside forces such as air resistance and friction between the base and the surface of the ice, angular momentum must remain constant. When one component such as the distance from the centre of gravity of the arm to the centre of rotation of the body is decreased, then there must be a corresponding increase in another component, the angular velocity and vice versa. Therefore when the arm’s centre of gravity is drawn in, the angular velocity is increased sufficiently so that the arm’s new centre of gravity traverses in the same given time period, a distance equal to that which it would have done along the wider original circle.

Coaches can easily work out for themselves the advantages in the rotational value of the short-arm loops and the desirability of working on these in preference to the long-arm strokes, unless the physique of their player is particularly suited to this latter area. The principle is of especial interest when working in the girls’ and women’s game where our subjects have much less body strength and need to use this as effectively as possible. Obviously a faster and shorter arm movement with good rotation will put much less stress on the back area while producing a very effective stroke.